I have a question. Are you saying that the fan runs when he starts Notes, but that if he closes the Notes client, and then restarts it, the fan does not act the same way? Is this the pattern each time he starts Notes, or an intermittent problem?
The first thing that comes to mind when the fan is running but there does not appear to be a cause for it is the SMC (System Management Controller). The following describes how to reset the SMC: https://support.apple.com/en-us/HT201295